PDF: Fix missing character when selecting backwards

pdf/pdfium/pdfium_engine.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "pdf/pdfium/pdfium_engine.h"
 
 #include <math.h>
 
 #include "base/json/json_writer.h"
 #include "base/logging.h"
@@ skipping 1845 matching lines @@
     for (int i = selection_[last].page_index() + 1; i < page_index; ++i) {
       selection_.push_back(PDFiumRange(pages_[i], 0,
                            pages_[i]->GetCharCount()));
     }
 
     int count = pages_[selection_[last].page_index()]->GetCharCount();
     selection_[last].SetCharCount(count - selection_[last].char_index());
     selection_.push_back(PDFiumRange(pages_[page_index], 0, char_index));
   } else {
     // Selecting into the previous page.
-    selection_[last].SetCharCount(-selection_[last].char_index());
+    // The selection's char_index is 0-based, so the character count is one
+    // more than the index. The character count needs to be negative to
+    // indicate a backwards selection.
+    selection_[last].SetCharCount(-(selection_[last].char_index() + 1));
 
     // First make sure that there are no gaps in selection, i.e. if mousedown on
     // page three but we only get mousemove over page one, we want page two.
     for (int i = selection_[last].page_index() - 1; i > page_index; --i) {
       selection_.push_back(PDFiumRange(pages_[i], 0,
                            pages_[i]->GetCharCount()));
     }
 
     int count = pages_[page_index]->GetCharCount();
     selection_.push_back(
@@ skipping 2038 matching lines @@
     double* height) {
   FPDF_DOCUMENT doc = FPDF_LoadMemDocument(pdf_buffer, pdf_buffer_size, NULL);
   if (!doc)
     return false;
   bool success = FPDF_GetPageSizeByIndex(doc, page_number, width, height) != 0;
   FPDF_CloseDocument(doc);
   return success;
 }
 
 }  // namespace chrome_pdf